Spectral binaries of brown dwarfs

Screen shot 2013-08-22 at 2.02.36 AMHow do brown dwarfs form? Some theories point to a star-like birth, accreting material from a molecular cloud, while some others point to a planet-like formation from a pre-stellar disk. Either way, the essential mechanisms for brown dwarf formation remain under debate by theorists. Given the astronomical timelines of star formation (1-10 million years), we cannot witness the formation process in action, but we can study its consequences on the statistical properties of the systems created.

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Orbital Artwork Earns Award

We normally think of orbits as the paths of satellites going around the Earth, or planets going around their host star, in both cases caused by the gravitational attraction between the two bodies. But the stars themselves also orbit within and around our collective systems of stars, the Milky Way Galaxy. In this case, the gravitational force is a cumulative attraction distributed among other stars, gas, dust and dark matter in the Galaxy, the last making up about 95% of the mass of our Galaxy. While we don’t have the longevity to observe the roughly quarter-million-year orbits of stars like the Sun, we can predict them using basic laws of physics.

In 2009, Adam was investigating the kinematics and Galactic orbits of several dozen low-temperature subdwarfs (metal-poor stars that likely formed early in our Galaxy’s history), and generated a visualization of these orbits for a press release at the American Astronomical Society meeting in Pasadena.  Here’s one of the images from this release:

And here’s a movie generated for the press conference, tracing the path of one of the “diving” stars LST 1610-0040 (note that slow down as the star passes the region of the Sun and the radio broadcast sphere around Earth, inspired by the opening sequence in the movie Contact):

 

A few years later, Adam decided to look a larger sample, over 500 L-type dwarfs discovered by colleague Sarah Schmidt in the Sloan Digital Sky Survey. Schmidt had measured tangential (proper) and radial motions, and combining these with distance estimates it is possible to predict the orbits of these stars. Adam mapped the million-year motions of these stars as they travelled around the Galaxy to produce the following pictures:

Computed Galactic orbits of 500 L dwarfs as viewed from above the Galactic plane.

Computed Galactic orbits of 500 nearby L dwarfs as viewed from above the Galactic plane. Most are confined to the same annulus that the Sun occupies in its orbit, although there are some far flung stars that happen to be local today.

Computed Galactic orbits of 500 L dwarfs as viewed from along the mid-plane of the Galaxy.

Computed Galactic orbits of 500 L dwarfs as viewed from along the mid-plane of the Galaxy. Again, most are confined to this mid-plane, with a rare set of stars on highly inclined orbits taking them hundreds to thousands of light-years above and below the plane.

 

Computed Galactic orbits of 500 L dwarfs mapped into cylindrical coordinates (radius from the Galactic center and vertically through the Galactic poles).  The Sun resides at the densest concentration of orbit lines.

Computed Galactic orbits of 500 L dwarfs mapped into cylindrical coordinates (radius from the Galactic center and vertically through the Galactic poles). Here we discern distinct patterns of orbits, from “box-type” (constrained to a narrow range of radii and heights) to “comet-type” (almost purely radial) to “halo” (large deflections away from the plane. The Sun resides at the densest concentration of orbit lines.

 

These images earned 2nd prize in the 2011 Art in Science competition at UCSD, and was used as cover artwork for the 6th Annual Artfest 55.

Observations of Luhman 16AB: A Brown Dwarf Binary at 2 pc

Early in March 2013, Kevin Luhman announced his discovery of a pair of brown dwarfs only 2 pc (6 light-years) from the Sun, the 3rd closest system to us after the α/Proxima Centauri system and Barnard’s Star. This remarkable find was buried in survey data going back 35 years, but elucidated with the mid-infrared sensitivity of the Wide-field Infrared Survey Explorer (WISE) and the object’s very high proper motion (2.8 arcseconds/year, or just under 0.1 degrees/century).  Using optical spectroscopy, Luhman found that the brighter of the two components had a late-L spectral type, suggesting that the system might straddle the transition between L dwarf and T dwarf spectral classes.  Knowing home much we like this really cool transition, we jumped into action.

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